DE102014223533A1 - Method and device for operating an exhaust-driven charging device with electromotive assistance - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (2) with an exhaust gas driven charging device (6) having electromotive assistance (64), comprising the following steps: - predetermining (S1) a desired charge pressure in a boost pressure section (46) on the output side Compressor (63) of the charging device (6) depending on a current load request; - Determining (S2) of a compressor mass flow through a compressor (63) of the charging device (6) depending on the predetermined desired boost pressure; - adjusting (S4) the compressor mass flow rate through the compressor (63) by utilizing exhaust enthalpy of combustion exhaust gas of the internal combustion engine (2) and the electromotive assistance (64); - Controlling (S3) of a recirculation valve (71) for allowing a circulating air mass flow in a return air line (7) connecting an output side and an input side of the compressor (63).

Description

Technical area

The invention relates to exhaust-driven charging devices with electromotive assistance. In particular, the present invention relates to measures for increasing the dynamics of an internal combustion engine by means of an electric motor assisted exhaust gas driven charging device.

State of the art

Exhaust-driven superchargers, so-called exhaust gas turbochargers, are used to provide increased boost pressure in an air supply system for an internal combustion engine. These convert an exhaust gas enthalpy provided by the combustion exhaust gases into mechanical energy. The mechanical energy is provided as rotational energy and used to drive a compressor. The compressor draws in ambient air and provides it in a boost section of the air supply system at a boost pressure greater than ambient pressure.

If the exhaust enthalpy is low, in particular at low speeds or loads of the internal combustion engine, and is therefore insufficient to provide a boost pressure required after an increase in the load requirement, concepts are known for coupling the exhaust-driven charging device to an electric motor. The electric motor then serves as a support for the acceleration (start-up) of the charging device by providing an additional torque.

One form of such a charging device is a coupling of the charging device with a media gap motor, in which the transmission of the magnetic fields between a stator and a rotor via the input side air gap of the sucked through the compressor ambient air.

By using the exhaust-driven charging device with electromotive support a higher spontaneity can be achieved, so that when sudden increase in the load request faster provision of the required boost pressure is possible.

In the case of a purely exhaust gas-driven charging device, the internal combustion engine usually reaches a full-load torque for a corresponding load request, starting from a lower rpm range, only between 3 to 5 seconds. In electric assisted charging devices, this time can be shortened to about 1.5 to 2 seconds, however, the required load torque is expected by the driver to be the appropriate dynamic response after one second at the latest.

Disclosure of the invention

According to the invention, a method for operating an internal combustion engine with an exhaust gas-driven charging device with electromotive assistance according to claim 1 as well as a device and an engine system according to the independent claims are provided.

Further embodiments are specified in the dependent claims.

• – Vorgeben eines Soll-Ladedrucks in einem Ladedruckabschnitt ausgangsseitig eines Verdichters der Aufladeeinrichtung abhängig von einer momentanen Lastanforderung;
• – Ermitteln eines Verdichtermassenstroms durch einen Verdichter der Aufladeeinrichtung abhängig von dem vorgegebenen Soll-Ladedruck;
• – Einstellen des Verdichtermassenstroms durch den Verdichter durch Nutzung von Abgasenthalpie von Verbrennungsabgas des Verbrennungsmotors und der elektromotorischen Unterstützung;
• – Ansteuern eines Umluftventils zum Zulassen eines Umluftmassenstroms in einer eine Ausgangsseite und eine Eingangsseite des Verdichters fluidisch verbindende Umluftleitung.

According to a first aspect, a method is provided for operating an internal combustion engine with an exhaust gas-driven charging device with electromotive assistance, comprising the following steps:

• - Specifying a target boost pressure in a boost pressure section on the output side of a compressor of the charging device depending on a current load request;
• - Determining a compressor mass flow through a compressor of the charging device depending on the predetermined target boost pressure;
• - Setting the compressor mass flow through the compressor by using exhaust enthalpy of combustion exhaust gas of the engine and the electromotive assistance;
• - Controlling a recirculation valve for allowing a circulating air mass flow in an output side and an input side of the compressor fluidly connecting recirculation line.

An idea of the above method is to provide a pre-flow strategy for an electromotive assist exhaust driven supercharger that uses a recirculation valve that connects a downstream side of the supercharger of the supercharger to an upstream side. To enable a quick build-up of the boost pressure, it is provided to control the recirculation valve so that a minimum mass flow of air through the compressor in the recirculation air line is achieved. In this way, fresh air delivered by the compressor is partially recirculated through the recirculation valve to the input side of the compressor, i. attributed to the upstream side of the charging device.

The setting of the air recirculation valve is made dependent on a required setpoint feed forward pressure. This results in the compressor map an operating point with an air mass flow through the compressor, which is just selected so high that it is guaranteed that no compressor pumps occurs. Thus, an air mass flow through the recirculation valve results as the difference of the compressor mass flow and the air mass flow, which is required by the internal combustion engine at the current operating point. The opening cross section of the recirculation valve can then be determined via conventional valve models, for example taking into account a differential pressure, a charge air temperature and the like.

The required speed of the compressor is determined depending on the compressor mass flow from a given compressor map and electrically controlled by means of the electromotive assistance.

For a spontaneous torque request, the recirculation valve can be completely closed and the electrical control can be increased until the new boost pressure setpoint is reached. As soon as the necessary exhaust gas enthalpy for operating the charging device for providing the necessary charge pressure is available, the electrical assistance can be correspondingly reduced.

By providing electrical support to the charging device and promoting increased mass air flow at a low load or part load operating point, the ability to close the recirculation valve in the event of a sudden load request can result in faster buildup of boost by closing the recirculation valve. This allows a higher dynamics of the internal combustion engine, so that a sudden request for an increased torque can be followed faster than would be possible with electromotive assisted charging without recirculation valve.

Furthermore, the target boost pressure can be determined as a function of a specific operating point of the internal combustion engine, wherein the target boost pressure can result from a static operating point of the internal combustion engine or as a target forward boost pressure, which is set in anticipation of an upcoming increase in load.

In particular, the compressor mass flow through the compressor of the charging device can be determined as the limit compressor mass flow at which no compressor pumping is currently taking place, or as the limit compressor mass flow minus a predetermined offset, depending on the preset desired boost pressure.

It may be provided that when a compressor mass flow is determined which is greater than the air mass flow, which is absorbed by the internal combustion engine, the recirculation valve is controlled so that the circulating air mass flow corresponds to a difference of the compressor mass flow and an engine air mass flow through the internal combustion engine.

According to one embodiment, adjusting the compressor mass flow through the compressor may be performed in response to a supercharger speed dependent on the compressor mass flow, wherein the speed of the supercharger is adjusted and / or regulated by driving the electromotive assistance.

Furthermore, when a sudden increase in load is requested, an efficiency of the turbine of the charging device can be increased.

Alternatively or additionally, when a sudden load increase is requested, the recirculation valve is closed or an opening cross-section of the recirculation valve can be reduced and in particular the electromotive assistance activated or driven with higher power.

It can be provided that, in the case of a requested load reduction, the recirculation valve in the recirculation line is opened further.

According to a further aspect, an apparatus, in particular a control unit, for operating an internal combustion engine with an electromotive assisted exhaust-gas-charged charging device is provided, the device being designed to carry out one of the above methods.

• – einen Verbrennungsmotor;
• – eine abgasgetriebene Aufladeeinrichtung mit elektromotorischer Unterstützung, die ausgebildet ist, um einen Verdichtermassenstrom durch einen Verdichter der Aufladeeinrichtung mithilfe einer bereitgestellten Abgasenthalpie von Verbrennungsabgas des Verbrennungsmotors und mithilfe eines Elektromotors einzustellen;
• – eine Umluftleitung mit einem variabel ansteuerbaren Umluftventil, um Ladeluft von einer Ausgangsseite zu einer Eingangsseite des Verdichters zurückzuführen; und
• – die obige Vorrichtung.

In another aspect, an engine system is provided, comprising:

• An internal combustion engine;
• An electromotive assisted exhaust gas supercharger configured to adjust a compressor mass flow through a supercharger of the supercharger using a provided exhaust enthalpy of combustion exhaust gas of the internal combustion engine and by means of an electric motor;
• - A recirculation line with a variably controllable recirculation valve to return charge air from an output side to an input side of the compressor; and
• - The above device.

Furthermore, the recirculation line may be configured to recirculate charge air from an area of the exit side of the compressor located downstream of an intercooler.

Brief description of the drawings

Embodiments of the present invention will be explained below with reference to the accompanying drawings. Show it:

1 a representation of an engine system with an electric motor assisted exhaust gas driven charging device;

2 a flowchart for illustrating a method for operating the engine system of 1 ,

Description of embodiments

In 1 is schematically an engine system 1 shown. The engine system 1 includes an internal combustion engine 2 with several cylinders 3 , The internal combustion engine 2 can be configured for example as a gasoline engine.

The internal combustion engine 2 Air is supplied via an air supply system 4 supplied, and combustion exhaust gases from the cylinders 3 of the internal combustion engine 2 be via an exhaust exhaust tract 5 dissipated. In the air supply system 4 and in the exhaust discharge tract 5 is a charging device 6 intended. The charging device 6 is with the exhaust exhaust tract 5 coupled to convert exhaust enthalpy of combustion exhaust gas into mechanical energy. The mechanical energy is used to supply ambient air in the air supply system 4 to condense.

The charging device has a turbine for this purpose 61 on in the exhaust discharge tract 5 is provided to the present in the exhaust gas exhaust gas enthalpy in a rotational movement of a shaft 62 implement. The turbine wheel of the turbine 61 can be designed to increase the dynamics of an inertia reducing material, such as titanium aluminide.

The wave 62 the charging device 6 is with a compressor 63 coupled, which depends on the rotation of the shaft 62 provides a compaction power to ambient air via an input-side section 41 to suck in and under a boost pressure in an output-side section 42 to provide. The input-side section 41 of the air supply system 4 is still with an air filter 43 provided that filters the intake fresh air.

In the output section 42 of the air supply system 4 is a throttle 44 provided between a boost pressure section 46 and a suction pipe section 47 , the parts of the output section 42 represent, is arranged. The throttle 44 serves to supply air to the cylinders 3 of the internal combustion engine 2 from the boost pressure section 46 to control.

The wave 62 is with an electric motor 64 (electromotive assistance) coupled, which adds an additional torque to the shaft 62 can muster to increase a compaction power electric motor. The electromotive assisted charging device 6 For example, it can be implemented with a so-called media gap motor located at the input side of the compressor 63 is arranged, wherein the transmission of the magnetic fields of the stator or rotor of the electric motor 64 takes place via the air gap of the sucked fresh air, ie the fresh air sucked in flows through an air gap between the stator and the rotor of the electric motor.

The charging device may further include a wastegate valve 65 in a bypass line 66 be provided. The bypass line 66 connects input side and output side of the turbine 61 , so that depending on a control of the wastegate valve 65 an efficiency of the turbine 61 can be adjusted. In particular, it is stated what proportion of the exhaust gas enthalpy into kinetic energy, ie in rotational energy of the shaft 62 is implemented. Instead of the wastegate valve 65 in the bypass line 66 Also, a VTG (VTG: Variable Turbine Geometry) actuator may be provided to increase the efficiency of the turbine 61 adjust or adjust the proportion of converted into mechanical energy exhaust enthalpy.

It is a control unit 10 provided that the internal combustion engine depending on state variables of the engine system 1 operates. As state variables, for example, a speed of the internal combustion engine 2 , a boost pressure of the compressed fresh air (charge air) in the boost pressure section 46 , a charge air temperature of the charge air in the boost pressure section 46 , an exhaust gas temperature of the exhaust gases emitted, an intake air mass flow on the input side of the compressor 63 and similar state variables can be detected or modeled by corresponding sensors.

The control unit 10 is configured to dependent on the detected and provided state variables positioner, such as a throttle actuator for setting the throttle 44 , Injectors for supplying fuel (not shown), the wastegate valve 65 , the electric motor 64 and the like to control the internal combustion engine 2 to control according to a predetermined target torque.

It is still a recirculation line 7 provided in which a recirculation valve 71 is arranged. The air valve 71 can be variably or continuously, ie with variable opening cross-section, are controlled, so that a predeterminable flow cross-section can be adjusted. The variably adjustable recirculation valve 71 can in particular be set with at least three different opening cross sections, such as completely open, fully closed and partially open. The variably adjustable recirculation valve 71 can be adjusted continuously or in steps.

The recirculation valve 71 can be pneumatically, but preferably made or operated electrically. Due to the possibility of variable or continuous control of the recirculation valve 71 can the required boost pressure in the boost pressure section 46 with the lowest possible air mass flow through the compressor 63 be achieved without it comes to a compressor pumps. This will increase the power consumption through the compressor 63 reduced to a minimum.

In the charge air section 46 can be a charge air cooler 45 be provided, which by the compression in the compressor 63 heated charge air cools. This allows the density in the charge air section 46 be increased charge air, so that a higher air charge in the cylinders 3 of the internal combustion engine 2 can be achieved.

The recirculation line 7 can be in an area of the charge air section 46 downstream of the intercooler 45 and upstream of the throttle 44 lead and this with an input-side section 41 connect. Thus, from the compressor 63 Promoted fresh air in the charge air section 46 is provided, via the recirculation line 7 and an at least partially open recirculation valve 71 in the input-side section 41 of the air supply system 4 to be led back.

By the arrangement of the recirculating air line 7 so that the charge air is taken downstream of the intercooler and to the input side of the compressor 63 can be returned, both overheating of the air delivered in the circle at an open recirculation valve 71 as well as a pump of the compressor 63 be excluded. Ideally, the intercooler 45 Type of air-water, so that it remains cool even when the vehicle is stationary, including the main radiator or fan.

The control of the recirculation valve 71 can through the control unit 10 according to one of the following with reference to the flowchart of 2 described method for operating an engine system with an electric motor assisted exhaust gas driven charging device done.

In step S1, a desired boost pressure is determined at a certain operating point of the internal combustion engine. The desired charge pressure may be from a defined operating point of the internal combustion engine 2 , in particular a static operating point result. Alternatively, as desired boost pressure, a so-called target forward charge pressure can be set, which is set in anticipation of an impending increase in load, ie, a sudden increase in the required target torque. Depending on the operating mode, the setpoint feed forward pressure can be permanently provided. The setpoint pre-charge pressure can also be preset only if it is detected that or if a sudden increase in the required setpoint torque is imminent. Indications for a potentially increasing load increase or starting operations are known from the prior art and can be derived, for example, from signals of the clutch, the gear selection, a radar sensor system, a traffic signal device and the like. In addition, there is the possibility of the flow speed of the compressor 63 or to adjust the set target boost pressure and the resulting target boost pressure adaptive to the driver type.

Depending on the desired desired boost pressure is in step S2 using a predetermined compressor map for the compressor 63 determined a lowest possible compressor mass flow at which just no compressor pumping occurs. The operating point for the compressor 63 , in which just no compressor pumps, is indicated by a surge limit or a limit compressor mass flow, in particular determined by the predetermined compressor map. The lowest possible compressor mass flow can be determined according to or dependent on the limit compressor mass flow, including an applicable safety distance (safety tolerance), ie minus a predetermined offset.

Especially at low speeds of the engine 2 can result in a necessary compressor mass flow, which is greater than the air mass flow, in the cylinder 3 of the internal combustion engine 2 is sucked.

The difference between the compressor mass flow and the engine air mass flow into the engine 2 sucked air determines the circulating air mass flow through the recirculation air line 7 and the recirculation valve 71 , The engine air mass flow is determined by the displacement of the cylinder and the speed of the engine 2 , So that the circulating air mass flow through the recirculation valve 71 can flow, in step S3, a corresponding opening cross-section of the recirculation valve 71 determined and set. The determination of the opening cross-section of the recirculation valve 71 can by conventional methods, such as a valve model involving a pressure difference across the recirculation valve 71 and a charge air temperature through the air circulation valve 71 flowing air are determined.

In order to set the compressor mass flow in step S4, the required rotational speed of the charging device 6 (or the compressor 63 ) determined accordingly and this with the help of the wastegate valve 65 and the electric motor 64 adjusted or regulated accordingly. This is done with the help of the control unit 10 , In particular, the charge is by the electric motor 64 supported if the exhaust enthalpy is insufficient to provide the required compressor capacity. The electric motor 64 can be used in particular for acceleration processes for the shaft 62 to support the determined speed of the charger 6 set as soon as possible.

In step S5 it is checked whether a sudden increase in a setpoint torque is specified. If this is the case (alternative: yes), then the method is continued with step S6, otherwise (alternative: no) is returned to step S1.

If a sudden increase in the requested setpoint torque is specified, then in step S6 the throttle valve can 44 be opened and the wastegate valve 65 getting closed. By closing the wastegate valve 65 All of the exhaust gas enthalpy available is converted into kinetic energy to drive the compressor 63 implemented. By opening the throttle 44 is achieved that the air mass flow in the internal combustion engine 2 is increased, so that the air charge increases and thereby the exhaust enthalpy also increases.

Furthermore, in step S7, the electric motor 64 maximum actuated to a determined or required for the provision of a new target boost pressure speed of the compressor 63 reach as fast as possible.

Simultaneously, in step S7, the recirculation valve 71 closed or reduced its opening cross-section and the previously by the recirculation line 7 flowing circulating air mass flow is now at least partially immediately available to build up the required target boost pressure available. According to the boost pressure control can now control the electric motor 64 be adapted to overshoot the achieved boost pressure, in particular an overshoot of the speed of the charging device 6 to avoid. In particular, it can be provided that the control of the electric motor 64 is reduced (ie the supporting torque of the electric motor 64 is reduced), before the opening cross-section of the wastegate valve 65 is reduced, reducing the proportion of exhaust enthalpy, resulting in mechanical energy for driving the compressor 63 is reduced.

To reduce a high charge pressure after a sudden decrease in the required setpoint torque, as known from the prior art, the recirculation valve 71 in the recirculation line 7 be opened so that a compressor mass flow through the compressor 63 is maintained and so a compressor pumps can be avoided.

Claims (13)

Method for operating an internal combustion engine ( 2 ) with an exhaust gas driven charging device ( 6 ), which has electromotive assistance ( 64 ), comprising the following steps: predetermining (S1) a desired charge pressure in a charge pressure section ( 46 ) on the output side of a compressor ( 63 ) of the charging device ( 6 ) depending on a current load request; Determining (S2) a compressor mass flow through a compressor ( 63 ) of the charging device ( 6 ) depending on the predetermined desired boost pressure; Adjusting (S4) the compressor mass flow through the compressor ( 63 ) by using exhaust enthalpy of combustion exhaust gas of the internal combustion engine ( 2 ) and electromotive assistance ( 64 ); - control (S3) of a recirculation valve ( 71 ) for allowing a circulating air mass flow in an output side and an input side of the compressor ( 63 ) connecting recirculating air line ( 7 ). The method of claim 1, wherein the desired boost pressure depending on a specific operating point of the internal combustion engine ( 2 ) is determined, wherein the target boost pressure results as a target forward boost pressure, which is set in anticipation of a pending increase in load. Method according to claim 1 or 2, wherein the compressor mass flow through the compressor ( 63 ) of the charging device ( 6 ) depending on the predetermined target boost pressure as the limit compressor mass flow at which no compressor pumps currently occurs, or is determined as the limit compressor mass flow minus a predetermined offset. Method according to one of claims 1 to 3, wherein, when a compressor mass flow is determined, which is greater than the mass air flow, of the internal combustion engine ( 2 ), the recirculation valve ( 71 ) is controlled so that the circulating air mass flow of a difference of the compressor mass flow and an engine air mass flow through the internal combustion engine ( 2 ) corresponds. Method according to one of claims 1 to 4, wherein adjusting the compressor mass flow through the compressor ( 63 ) depending on a dependent of the compressor mass flow speed of the charging device ( 6 ), wherein the speed of the charging device ( 6 ) by driving the electromotive assistance ( 64 ) is adjusted and / or regulated. Method according to one of claims 1 to 5, wherein, when a sudden load increase is requested, an efficiency of the turbine ( 61 ) of the charging device ( 6 ) is increased. Method according to one of claims 1 to 6, wherein, when a sudden load increase is requested, the recirculation valve ( 71 ) is closed or an opening cross-section of the recirculation valve ( 71 ) and in particular the electromotive assistance ( 64 ) is activated or controlled with higher power. Method according to one of claims 1 to 7, wherein at a requested load reduction, the recirculation valve ( 71 ) in the recirculation line ( 7 ) is opened further. Contraption ( 10 ), in particular control unit, for operating an internal combustion engine ( 2 ) with an exhaust gas driven charging device ( 6 ) with electromotive assistance ( 64 ), the device ( 10 ) is designed to carry out the method according to one of claims 1 to 8. Engine system ( 1 ) comprising: - an internal combustion engine ( 2 ); An exhaust gas driven charging device ( 6 ) with electromotive assistance ( 64 ) which is adapted to a compressor mass flow through a compressor ( 63 ) of the charging device ( 6 ) by means of a provided exhaust gas enthalpy of combustion exhaust gas of the internal combustion engine ( 2 ) and by means of an electric motor ( 64 ); - a recirculation line ( 7 ) with a variably controllable recirculation valve ( 71 ) to charge air from an output side to an input side of the compressor ( 63 ); and - an apparatus according to claim 9. Engine system ( 1 ) according to claim 10, wherein the recirculating air line ( 7 ) is designed to charge air from a region of the output side of the compressor ( 63 ), which is located downstream of a charge air cooler. Computer program, which, when executed in a data processing device, is adapted to carry out all the steps of a method according to one of Claims 1 to 8. A machine-readable storage medium on which a computer program according to claim 12 is stored.

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